Field of the Invention
The invention relates to an aluminium casting alloy which can be cast very well and also has a high strength in the hot state after a long operating duration at high operating temperatures.
Likewise, the invention relates to a component for combustion engines which is cast from an aluminium alloy. Such components are, in particular, cylinder heads or engine blocks.
Description of Related Art
Increasing requirements for, on the one hand, the engine power and, on the other hand, the minimisation of fuel consumption and weight, lead to higher and higher requirements for the mechanical and thermal resilience of engine components cast from aluminium alloys. Therefore, aluminium casting alloys which are suitable for the production of such components must have a high yield strength both at room temperature and at operating temperature, a high ultimate strain, a high thermal conductivity, a low thermal expansion, a high creep resistance, as well as favourable processing properties, which include a good fluidity and low hot cracking tendency. At the same time, these alloys should be able to be cast well in order to enable a reliable production of the castings.
A large number of material concepts is known with which these partially opposing requirements for aluminium casting materials of the type discussed here are fulfilled. These material concepts include aluminium casting alloys of the alloy groups Al—Si—Mg and Al—Si—Cu. In the case of these alloys, however, at operating temperatures of over 250° C., the coarsening of the hardening phase can occur as a consequence of diffusion of the elements contributing to the hardening, such as Cu, Mg and Zn, and thus, in conjunction with this, a strong reduction of the mechanical characteristic values occurs. The aim of the development of new alloys for the aluminium casting of components for combustion engines is therefore an optimised high temperature resistance (see article “Warmfeste Aluminiumgusslegierungen für Zylinderkopfe in direktem Wettbewerb” (Heat-resistant aluminium casting alloys for cylinder heads in direct competition), June 2009 GIESSEREIPRAXIS, pages 199-202).
It is known that by addition of a high amounts of Cu, the heat resistance of Al casting alloys can increase. One group of alloys which uses this positive influence of Cu on the heat resistance is known by the name “AlCu7xx”. Under this, for example, falls the alloy “AlCu7MnZr” which contains, besides Al and accompanying elements, (in % by weight) 6.72% Cu, 0.22% Zr, 0.11% Ti, 0.5% Mn as well as the traces of Fe, Mg and Zn which are attributable to impurities. The superior heat resistance of aluminium casting alloys of this type which have a Cu content, however, are faced with an increased hot cracking tendency and a greatly limited castability. Thus the AlCu7MnZr alloy specified above also proves to be practically uncastable.